Film manufacture



June 7, 1938. 5, J CARROLL 2,119,702

FILM MANUFACTURE Filed Aug. 7, 1936 FIG.1.

FIG.3.

INVENTOR. Stewart J. Carroll M d 1% m K tion or dope composed of a colloidal material, forming surface. I have found that when em- 10 Patented June 7, 1938 UNITED STATES PATENT OFFICE FILM MANUFACTURE Stewart J. Carroll, Rochester, N. Y., assignor, by

mesne assignments, to Eastman Kodak Company, Jersey City, N. J., a corporation of New Jersey Application August 7, 1936, Serial No. 94,835

4 Claims. (o1. 18-7-57) This invention relates to the manufacture of coating wheel or other devicecommonly employed sheets or films composed of cellulose esters and in the film industry. Other objects will appear ethers and various other colloidal materials. hereinafter. More particularly, the invention relates to a These objects are accomplished by the follow- 5 method of facilitating the removal of such sheets ing invention which, in its broader aspects, com- 5 or films from the surface upon which they are prises casting the film in the usual manner, causformed. ing the film to set by evaporating solvents there- As is well-known, various types of film and from and then applying a bead of liquid atthe sheeting are usually made by depositing a solupoint at which the film is stripped from the filmsuch as a cellulose ester or ether, in a thin layer ploying a wheel for casting the film, if a liquid on the surface of a slowly rotating wheel or drum, which is non-solvent with respect to the film maor by depositing the material on the surface of an terial, such as cold water, isplaced in the V- endless metallic band, removingsolvents from shaped opening formed betweenthe wheel surthe deposited material by means of heated air or face and the inner surface of the film 'as it 15 other coagulating media and finally stripping the leaves the wheel, the'film breaks away from the coagulated material from the film-forming sursurface sharply without sticking, stretching, orface in a continuous sheet. Notwithstanding that the production of snap lines in the product. the bulk of the solvent has been removed from the In the following examples and description I film when it reaches the point where it is stripped have set forth several of the preferred embodifrom the film-forming surface, it nevertheless remerits of my invention but they are included tains a small amount thereof. If this amount of merely for purposes of illustration and not as a solvent is above a certain critical value, the film limitation thereof. r

will strip steadily and cleanly from the coating In the accompanying drawing in which like surface, but the amount of solvent present in the reference characters refer to like parts, 25

film under such circumstances is much too high Fig. 1 is a schematic, elevational view of a mafor practical purposes, since it must be subsechine adapted for the production of films com quently removed before the film is fit for composed of colloidal materials such as cellulose demercial use. The removal of such considerable rivatives and the like, and illustrating the manamounts of residual solvent presents various disner in which the film is removed from the film- 3O advantages and are likely to cause defects in the forming surface in accordance with the present film structure itself. On the other hand, if the invention.

residual solvent content is below the critical value, Fig. 2 is an enlarged fragmentary view more the film adheres so tenaciously to the film-formfully illustrating the action of the liquid bead in ing surface that it can be removed therefrom only facilitating removal of the film from the filmby the application of considerable force. This forming surface; causes the film to strip from the surface in jerks, Fig. 3 is another fragmentary view similar to giving rise to the phenomenon known as snap that of Fig. 2 illustrating the use of a chill roll in lines on the film surface which renders it deconjunction with a liquid bead. I

40 fective for photographic and other uses where In carrying out my inventionI maintain a bead 40 practically perfect transparency is required. The of non-solvent liquid in the crevice between the adhesion may in some cases be so great as to stripped film and the surface upon whichit is 7 cause small portions of the film to be torn away formed. I have found that water, for example, from the main body of the material and left upon serves the purpose very well, although other non- 5 the film-forming surface. solvent liquids may be employed. I have found The present invention has as its principal obthat especially desirable results are obtained if ject to obviate the above-mentioned difliculties the water or other liquid is applied in a cool or in the manufacture of sheets or films from colloicold condition, the film apparently being cooled dal materials, such as cellulose derivatives and thereby and stripping more readily in that conthe like, and to provide a means whereby such dition. Supplemental cooling by means of a 50 films may be stripped from a film-forming surchill roll or other device applied as indicated in face without the production of snap lines or sim- Fig. 3 is sometimes desirable from the standpoint ilar optical defects. Another object is to provide of further increasing the ease of stripping. an improved method of stripping cellulose de- As indicated, the material employed for prorivative and other films from the surface of a ducing the bead should be a liquid which has no 55 substantial solvent action upon the material of which the film is formed and should, of course, be substantially non-corrosive with respect to the metallic surface of the coating wheel or other device upon which the film is formed. In the manufacture of cellulose derivative and other types of film I find that water serves the purpose especially well, since it has no solvent action on the film material. Furthermore, water has the added advantage that it exerts a slight solvent extracting or curing effect on the film. Other liquids which may be used in accordance with the invention are members of the aliphatic series of hydrocarbons, such as hexane, heptane, octane, etc; various aromatic hydrocarbons such as benzene and toluene. In connection with the stripping of cellulose acetate film, ethyl alcohol or methyl alcohol may be satisfactorily employed.

While I prefer to use cold water, that is, water cooled substantially below room temperature, the matter of temperature does not appear to be critical. In some cases it may even be desirable to use water at temperatures above room temperature, while in other cases the temperature of the liquid may be close to the freezing point. In either case the effect obtained is substantially the same, namely, perfect stripping of the film without sticking to the film-forming surface and without the production of snap lines or other undesirable defects in the film which would adversely affect its transparency.

At this point, it is desirable to point out that the action of the liquid bead is apparently not due to any difference between the temperature of the liquid and that of the film material. Its action is more akin to a mechanical action in that it causes the clean-cut separation of the film material from the coating surface independently of any thermal or chemical action. While I oifer no theoretical explanation to account for the phenomenon, it appears that the results obtained are due to some type of physical force acting between the liquid bead, the metal filmforming surface and the film material itself.

My invention will be'more readily understood by reference to the accompanying drawing. In Fig. l, the numeral 10 designates a coating wheel of a conventional type such as used in the film manufacturing industry. This wheel receives from the hopper H, a viscous solution or dope comprising a cellulose derivative such as cellulose nitrate or cellulose acetate dissolved in appropriate solvents. The dope is caused to How upon the polished wheel surface at such a depth and speed as will produce a finished film l3 of the desired thickness, the depth of the dope at the hopper, and indirectly the thickness of the film, being controlled by means of a gate l2 in known manner. The wheel rotates slowly in the direction indicated by the arrow, while a current of heated air or other coagulating media is circulated around the wheel surface, preferably in a direction counter-current to the direction of rotation, whereby solvents are removed from the film. The customary enclosure or housing for the wheel through which the air circulates is not shown in the drawing, being of a conventional design well-known in the art. The film is detached or stripped from the film-forming surface when the wheel I!) has passed through about three-fourths of a revolution, being guided over guide roll l4 and thence to an appropriate drying or curing apparatus (not shown).

In accordance with the invention, a suitable supply of water 'or other non-solvent liquid is supplied from a suitable source through the pipe l5 which terminates in an outlet IS, the flow of liquid being controlled by the valve [1. The water is permitted to drop from the outlet l6 into the V-shaped opening formed between the filmforming surface l8 and the inside surface of the film l3, thus maintaining a constant liquid head at approximately the exact point of stripping. The supply of liquid may be continuous or intermittent, this being immaterial so long as the bead is maintained. No great amount of liquid need be permitted to accumulate in the V, a relatively fine bead apparently being as effective as a large bead.

In Fig. 2, I have illustrated in enlarged section, the further action of the liquid bead in separating the film from the film-forming surface. It will be evident that in some way the theoretical explanation of which is not clear, the bead l9 has a very definite and positive action in splitting the film away from the film-forming surface. This is remarkable and wholly unexpected when one considers the fact that water is a very mobile and easily deformable liquid.

In Fig. 3, I have illustrated the stripping of a film by a method which involves both the application of the liquid bead and the use of a chill roll. In this method the liquid bead is maintained in the V-shaped opening between the film and the film-forming surface as previously described, but a cold roll 20, preferably a hollow roll supplied with a low temperature brine 2|, or other suitably cooled medium is applied to the outside surface of the film at the point of stripping. This tends further to harden or set the film before actual stripping occurs.

As indicated above, many changes may be made in the above method of carrying out the process herein described within the scope of my invention. Various types of liquids may be employed so long as they do not have any adverse solvent or other effect on either the film itself or the machinery. Water is eminently suitable for the purpose for the reasons previously alluded to. My invention is broadly applicable to the stripping of films made from various colloidal materials such as those composed of cellulose derivatives such as cellulose nitrate, cellulose acetate, cellulose propionate, cellulose butyrate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate stearate, the cellulose ethers, and many others. This method has also been found to be of particular importance in connection with the manufacture of films composed of resinous materials, particularly films of the vinyl or vinyl acetal types. These materials, due to their peculiar properties, present rather difficult problems of coating, stripping and curing which are overcome'by this invention.

It will also be evident that my invention is not limited to the stripping of films formed on wheel surfaces, but may also be applied to the manufacture of films by coating appropriate solutions on endless metallic bands, it being obvious that a bead of liquid may be maintained at the point of stripping in such devices as well as in the cas of casting wheel devices.

The facility with which a given film may be stripped from a casting surface depends upon a number of factors such as the particular type of cellulose derivative employed in the film, the type of solvent used in making up the film forming dope, the particular plasticizers used, the speed' of casting and the type of casting surface.

It will thus be readily understood that the critical solvent content of the film, that is, the amount of solvent which it may contain and still be made to strip cleanly from the casting surface, is variable. In some cases this critical solvent content may be close to zero, while in other cases it may be as high as 10 or 15%, but whether the amount is small or large, the application of the liquid head in accordance with my invention causes the film to strip cleanly and without snap lines. As a matter of fact, I have found that some types of dopes, particularly cellulose acetate dopes, when cast upon a glass surface, for example, tend to stick so tenaciously thereto that it is impossible to remove them from the casting surface by ordinary means without ruining the film. Nevertheless, such films may be quite readily removed by the application of a water bead in accordancewithmy invention, the bead causing the film to immediately lift from the surface without any adverse effects on the film surface.

What I claim is:

l. The process of producing a sheet or film which comprises casting a solution of a colloidal material in the form. of a film on a film-forming surface, removing solvent therefrom and stripping the film from the surface in a direction which provides an approximately V-shaped crevice between the film and the surface in which the vertex of the V is at least as low as any'other point in the V, and maintaining a supply of a non-solvent liquid in the crevice by gravity.-

2. The process of producing a sheet or film which comprises casting a solution of a colloidal material in the form of a film on a continuously I moving film-forming surface, removing solvent therefrom and stripping the film from the surface in a direction which provides an approximately V-shaped crevice between the film and the surface inwhich the vertex of the V is at least as low as any other point in the V, and maintaining a supply of a non-solvent liquid in the crevice by gravity.

3. The process of producing a sheet or film which comprises casting a solution of a water-insoluble colloidal material in the form of a film on a, continuously moving film-forming surface, removing solvent therefrom and stripping the film from the surface in a direction which provides an approximately V-shaped crevice between the film and the surface in which the vertex of the V is at least as low as any other point in the V, and maintaining a supply of water in the crevice by gravity.

4. The process of producing a sheet or film which comprising casting a solution of hydrocarhon-insoluble colloidal material in the form of a film on a continuously moving film-forming surface, removing solvent therefrom and stripping the film from the surface in a direction which provides an approximately V-shaped crevice between the film and the surface in which the vertex of the V is at least as low as any other 1 

